Surface area to volume ratio

• what are cells constantly doing?

  maintaining balance between the different environments within them and around them.
• where do exchanges between an organism and its surroundings occur?

  at the surfaces.
• what makes up the volume of an organism?

  cells.
• what in the body uses the materials absorbed in through the surface?

  the cells.
• in order to absorb enough required material quickly enough to supply the rest of the body, what must happen?

  the surfaces through which exchange takes place have to be large in relation to the volume of the organism as a whole.
• why can diffusions not be the sole source of exchange in larger organisns? why?

  it wouldn’t supply the organism with enough material quick enough bc lots of the body’s cells are some distance away from the exchange surfaces and diffusion to these inner walls would be hard and slow.
• what does it mean that smaller organisms have a reasonable ratio of surface area to volume?

  diffusion through the organisms’ surface could be sufficient to meet its needs.
• as organisms get bigger they have to adapt to aid their exchanges with their environment, why?


  as their volume increases at a quicker rate than the surface area does
• why have some organisms developed a flattened shape? eg?

  so all their cells are reasonably close to the exchange surfaces. eg: plants or flat fish.
• what are 3 examples of larger organisms developing specialist exchange systems?

  trachea in insects, lungs in mammals and gills in fish.
• why do the specialist exchange surfaces of larger organisms work?

  they comprise of additional exchange surfaces and help to increase the overall surface area to volume ratio.
• how do you calculate surface area of a cube?

  area of 1 side x 6 (cm2)
• how to calculate area of a square?

  height x width
• how to calculate volume of a cube?

  length x width x height (cm3)
• how to calculate surface area to volume ratio?

  surface area / volume
• as the size of an organism increases ??

  the ratio between surface area and volume quickly reaches parity before flipping the other way where the volume is far greater than the surface area and so diffusion through the organisms outer surface is not sufficient.
• look at this and learn it

  
• what do adaptations that allow larger organisms to exchange materials demonstrate?

  specific characteristics to achieve this, they provide a large surface area relative to the organisms volume, their actual exchange surfaces are thin allowing for optimum transfer, they are selectively permeable so are selective of the materials they allow to cross in either direction.
• how are diffusion gradients maintained? eg?

  by moving the environmental medium and the internal medium. eg: in mammals they are air and blood.
• look at this and learn

  
• how to calculate surface area of a sphere?

  SA = 4pi r^2
• how to calculate volume of a sphere?

  4/3 pie r^2
• volume meaning 


  the amount of 3D space occupied by an object.
• surface area meaning


  the total area of the surfaces of a 3 dimensional structure or organisms
• pi 


  a mathematical constant relating to spheres and circles
• diameter


  the distance from one edge of a sphere or circle to the opposite edge when passing through the centre.
• radius


  half the diameter, the distance from the centre of the sphere or circle to the edge or surface.
• when the size or volume of an organism is small.. (so?)

  ...the surface area to volume ratio is large. So, the organism can survive just bye changing materials by diffusion.
• how do single celled organisms use diffusion?

  they take in oxygen and remove carbon dioxide as they respire through the cell membrane just by diffusion.
• what issues do insects have?

  they are larger than a single cell and begin to have the problem that diffusion through their body surfaces aren't enough to keep up with the demand for oxygen or let them get rid of carbon dioxide fast enough.
• look and learn

  
• what is the tracheal system used for in insects?

  gas exchange.
• what is the design of an insects anatomy a careful balance between?

  the conservation of water and the need to exchange gases with the environment.
• what would an increased surface area do for insects?

  provide an increased surface area to lose water.
• what gas exchange system did insects develop?

  the tracheal system.
• what are the trachea?

  a network of tubes throughout the body of the insect that terminate on the surface at small opening called spiracles that can be opened and closed as needed.
• what is at the opposite end of the tracheae branch?

  the trachea branch out into tiny closed end tubes called tracheoles.
• what job do the tracheoles have?

  deliver oxygen from the air directly to the tissues of the insect.
• how do the tracheoles do their job?

  they create a short diffusion pathway that makes for efficient gas exchange with the insects surroundings.
• what are the 3 processes that the gases used and produced during respiration move in and out of the trachael system through?

  • following a diffusion gradient
  • mass transport
  • water in the tracheoles